The invention is related to a process and a device for detection of rotational speed of a rotating part using a magnet wheel connected to the rotating part.
For detecting the rotational speed of vehicle tires or other rotating parts, it is customary to attach to the rotating part a so-called magnet wheel which turns along with that part and has projecting teeth on its outer periphery that are distributed equidistantly around that periphery of the magnet wheel. An inductive sensor arranged near the outer periphery of the magnet wheel responds to changes of a magnetic field produced by it and produces in the ideal case a sinusoidal alternating current. The changes in the magnetic field are generated by the teeth and teeth gaps passing alternately through the sensor magnetic field. The frequency of this alternating current is proportional to the rotational speed of the rotating part. Such sensors are employed, for instance, to detect the wheel rotation speed of vehicles that are equipped with an antilocking or drive slippage controller.
Because of manufacturing tolerances, damage or contamination of the magnet wheel, the form of the alternating current produced by the inductive sensor frequently deviates in practice from the sinusoidal profile, which leads to inaccuracies in evaluating the signal represented by this alternating current. For instance, errors in the detected rotational speed will appear in use in conjunction with antilocking brake systems, which can then lead to a deterioration of the antilocking control.
In known devices the alternating current emitted by the inductive sensor is fed to a comparator, the square-wave output signal of which then likewise has interference. It was attempted to solve this problem by filtering the sensor signal, which is only possible to a limited extent, however, since the interference signals that appear usually lie in the same frequency range as the useful signal.